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Date:	Sat, 18 Jan 2014 11:13:53 -0800 (PST)
From:	dormando <dormando@...ia.net>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: ipv4_dst_destroy panic regression after 3.10.15

> On Fri, Jan 17, 2014 at 11:16 PM, dormando <dormando@...ia.net> wrote:
> >> On Fri, 2014-01-17 at 22:49 -0800, Eric Dumazet wrote:
> >> > On Fri, 2014-01-17 at 17:25 -0800, dormando wrote:
> >> > > Hi,
> >> > >
> >> > > Upgraded a few kernels to the latest 3.10 stable tree while tracking down
> >> > > a rare kernel panic, seems to have introduced a much more frequent kernel
> >> > > panic. Takes anywhere from 4 hours to 2 days to trigger:
> >> > >
> >> > > <4>[196727.311203] general protection fault: 0000 [#1] SMP
> >> > > <4>[196727.311224] Modules linked in: xt_TEE xt_dscp xt_DSCP macvlan bridge coretemp crc32_pclmul ghash_clmulni_intel gpio_ich microcode ipmi_watchdog ipmi_devintf sb_edac edac_core lpc_ich mfd_core tpm_tis tpm tpm_bios ipmi_si ipmi_msghandler isci igb libsas i2c_algo_bit ixgbe ptp pps_core mdio
> >> > > <4>[196727.311333] CPU: 17 PID: 0 Comm: swapper/17 Not tainted 3.10.26 #1
> >> > > <4>[196727.311344] Hardware name: Supermicro X9DRi-LN4+/X9DR3-LN4+/X9DRi-LN4+/X9DR3-LN4+, BIOS 3.0 07/05/2013
> >> > > <4>[196727.311364] task: ffff885e6f069700 ti: ffff885e6f072000 task.ti: ffff885e6f072000
> >> > > <4>[196727.311377] RIP: 0010:[<ffffffff815f8c7f>]  [<ffffffff815f8c7f>] ipv4_dst_destroy+0x4f/0x80
> >> > > <4>[196727.311399] RSP: 0018:ffff885effd23a70  EFLAGS: 00010282
> >> > > <4>[196727.311409] RAX: dead000000200200 RBX: ffff8854c398ecc0 RCX: 0000000000000040
> >> > > <4>[196727.311423] RDX: dead000000100100 RSI: dead000000100100 RDI: dead000000200200
> >> > > <4>[196727.311437] RBP: ffff885effd23a80 R08: ffffffff815fd9e0 R09: ffff885d5a590800
> >> > > <4>[196727.311451] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> >> > > <4>[196727.311464] R13: ffffffff81c8c280 R14: 0000000000000000 R15: ffff880e85ee16ce
> >> > > <4>[196727.311510] FS:  0000000000000000(0000) GS:ffff885effd20000(0000) knlGS:0000000000000000
> >> > > <4>[196727.311554] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> > > <4>[196727.311581] CR2: 00007a46751eb000 CR3: 0000005e65688000 CR4: 00000000000407e0
> >> > > <4>[196727.311625] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> > > <4>[196727.311669] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> >> > > <4>[196727.311713] Stack:
> >> > > <4>[196727.311733]  ffff8854c398ecc0 ffff8854c398ecc0 ffff885effd23ab0 ffffffff815b7f42
> >> > > <4>[196727.311784]  ffff88be6595bc00 ffff8854c398ecc0 0000000000000000 ffff8854c398ecc0
> >> > > <4>[196727.311834]  ffff885effd23ad0 ffffffff815b86c6 ffff885d5a590800 ffff8816827821c0
> >> > > <4>[196727.311885] Call Trace:
> >> > > <4>[196727.311907]  <IRQ>
> >> > > <4>[196727.311912]  [<ffffffff815b7f42>] dst_destroy+0x32/0xe0
> >> > > <4>[196727.311959]  [<ffffffff815b86c6>] dst_release+0x56/0x80
> >> > > <4>[196727.311986]  [<ffffffff81620bd5>] tcp_v4_do_rcv+0x2a5/0x4a0
> >> > > <4>[196727.312013]  [<ffffffff81622b5a>] tcp_v4_rcv+0x7da/0x820
> >> > > <4>[196727.312041]  [<ffffffff815fd9e0>] ? ip_rcv_finish+0x360/0x360
> >> > > <4>[196727.312070]  [<ffffffff815de02d>] ? nf_hook_slow+0x7d/0x150
> >> > > <4>[196727.312097]  [<ffffffff815fd9e0>] ? ip_rcv_finish+0x360/0x360
> >> > > <4>[196727.312125]  [<ffffffff815fda92>] ip_local_deliver_finish+0xb2/0x230
> >> > > <4>[196727.312154]  [<ffffffff815fdd9a>] ip_local_deliver+0x4a/0x90
> >> > > <4>[196727.312183]  [<ffffffff815fd799>] ip_rcv_finish+0x119/0x360
> >> > > <4>[196727.312212]  [<ffffffff815fe00b>] ip_rcv+0x22b/0x340
> >> > > <4>[196727.312242]  [<ffffffffa0339680>] ? macvlan_broadcast+0x160/0x160 [macvlan]
> >> > > <4>[196727.312275]  [<ffffffff815b0c62>] __netif_receive_skb_core+0x512/0x640
> >> > > <4>[196727.312308]  [<ffffffff811427fb>] ? kmem_cache_alloc+0x13b/0x150
> >> > > <4>[196727.312338]  [<ffffffff815b0db1>] __netif_receive_skb+0x21/0x70
> >> > > <4>[196727.312368]  [<ffffffff815b0fa1>] netif_receive_skb+0x31/0xa0
> >> > > <4>[196727.312397]  [<ffffffff815b1ae8>] napi_gro_receive+0xe8/0x140
> >> > > <4>[196727.312433]  [<ffffffffa00274f1>] ixgbe_poll+0x551/0x11f0 [ixgbe]
> >> > > <4>[196727.312463]  [<ffffffff815fe00b>] ? ip_rcv+0x22b/0x340
> >> > > <4>[196727.312491]  [<ffffffff815b1691>] net_rx_action+0x111/0x210
> >> > > <4>[196727.312521]  [<ffffffff815b0db1>] ? __netif_receive_skb+0x21/0x70
> >> > > <4>[196727.312552]  [<ffffffff810519d0>] __do_softirq+0xd0/0x270
> >> > > <4>[196727.312583]  [<ffffffff816cef3c>] call_softirq+0x1c/0x30
> >> > > <4>[196727.312613]  [<ffffffff81004205>] do_softirq+0x55/0x90
> >> > > <4>[196727.312640]  [<ffffffff81051c85>] irq_exit+0x55/0x60
> >> > > <4>[196727.312668]  [<ffffffff816cf5c3>] do_IRQ+0x63/0xe0
> >> > > <4>[196727.312696]  [<ffffffff816c5aaa>] common_interrupt+0x6a/0x6a
> >> > > <4>[196727.312722]  <EOI>
> >> > > <4>[196727.312727]  [<ffffffff8100a150>] ? default_idle+0x20/0xe0
> >> > > <4>[196727.312775]  [<ffffffff8100a8ff>] arch_cpu_idle+0xf/0x20
> >> > > <4>[196727.312803]  [<ffffffff8108d330>] cpu_startup_entry+0xc0/0x270
> >> > > <4>[196727.312833]  [<ffffffff816b276e>] start_secondary+0x1f9/0x200
> >> > > <4>[196727.312860] Code: 4a 9f e9 81 e8 13 cb 0c 00 48 8b 93 b0 00 00 00 48 bf 00 02 20 00 00 00 ad de 48 8b 83 b8 00 00 00 48 be 00 01 10 00 00 00 ad de <48> 89 42 08 48 89 10 48 89 bb b8 00 00 00 48 c7 c7 4a 9f e9 81
> >> > > <1>[196727.313071] RIP  [<ffffffff815f8c7f>] ipv4_dst_destroy+0x4f/0x80
> >> > > <4>[196727.313100]  RSP <ffff885effd23a70>
> >> > > <4>[196727.313377] ---[ end trace 64b3f14fae0f2e29 ]---
> >> > > <0>[196727.380908] Kernel panic - not syncing: Fatal exception in interrupt
> >> > >
> >> > >
> >> > > ... bisecting it's going to be a pain... I tried eyeballing the diffs and
> >> > > am trying a revert or two.
> >> > >
> >> > > We've hit it in .25, .26 so far. I have .27 running but not sure if it
> >> > > crashed, so the change exists between .15 and .25.
> >> >
> >> > Please try following fix, thanks for the report !
> >> >
> >> > diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> >> > index 25071b48921c..78a50a22298a 100644
> >> > --- a/net/ipv4/route.c
> >> > +++ b/net/ipv4/route.c
> >> > @@ -1333,7 +1333,7 @@ static void ipv4_dst_destroy(struct dst_entry
> >> > *dst)
> >> >
> >> >     if (!list_empty(&rt->rt_uncached)) {
> >> >             spin_lock_bh(&rt_uncached_lock);
> >> > -           list_del(&rt->rt_uncached);
> >> > +           list_del_init(&rt->rt_uncached);
> >> >             spin_unlock_bh(&rt_uncached_lock);
> >> >     }
> >> >  }
> >> >
> >>
> >> Problem could come from this commit, in linux 3.10.23,
> >> you also could try to revert it
> >>
> >> commit 62713c4b6bc10c2d082ee1540e11b01a2b2162ab
> >> Author: Alexei Starovoitov <ast@...mgrid.com>
> >> Date:   Tue Nov 19 19:12:34 2013 -0800
> >>
> >>     ipv4: fix race in concurrent ip_route_input_slow()
> >>
> >>     [ Upstream commit dcdfdf56b4a6c9437fc37dbc9cee94a788f9b0c4 ]
> >>
> >>     CPUs can ask for local route via ip_route_input_noref() concurrently.
> >>     if nh_rth_input is not cached yet, CPUs will proceed to allocate
> >>     equivalent DSTs on 'lo' and then will try to cache them in nh_rth_input
> >>     via rt_cache_route()
> >>     Most of the time they succeed, but on occasion the following two lines:
> >>         orig = *p;
> >>         prev = cmpxchg(p, orig, rt);
> >>     in rt_cache_route() do race and one of the cpus fails to complete cmpxchg.
> >>     But ip_route_input_slow() doesn't check the return code of rt_cache_route(),
> >>     so dst is leaking. dst_destroy() is never called and 'lo' device
> >>     refcnt doesn't go to zero, which can be seen in the logs as:
> >>         unregister_netdevice: waiting for lo to become free. Usage count = 1
> >>     Adding mdelay() between above two lines makes it easily reproducible.
> >>     Fix it similar to nh_pcpu_rth_output case.
> >>
> >>     Fixes: d2d68ba9fe8b ("ipv4: Cache input routes in fib_info nexthops.")
> >>     Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>
> >>     Signed-off-by: David S. Miller <davem@...emloft.net>
> >>     Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >>
> >
> > Heh. I spent an hour squinting at the difflog from .15 to .25 and this was
> > my best guess. I have a kernel running in production with only this
> > reverted as of ~5 hours ago. Won't know if it helps for a day or two.
> >
> > I'm building a kernel now with your route patch, but 62713c4 *not*
> > reverted, which I can throw on a different machine. Does this sound like a
> > good idea?
>
> the traces of your crash don't look similar to dst leak that was fixed by
> commit 62713c4...
>
> To trigger the 'fix' logic of the 62713c4 add the following diff:
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index f6c6ab1..8972676 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1259,7 +1259,7 @@ static bool rt_cache_route(struct fib_nh *nh,
> struct rtable *rt)
>                 p = (struct rtable **)__this_cpu_ptr(nh->nh_pcpu_rth_output);
>         }
>         orig = *p;
> -
> +       mdelay(100);
>         prev = cmpxchg(p, orig, rt);
>         if (prev == orig) {
>                 if (orig)
>
> I've been running with it for a day without issues.
> Note that it will stress both 'input' and 'output' ways of adding dsts to
> rt_uncached list...
> and 'output' was there for ages.
>
> If mdelay() helps to reproduce it in minutes instead of days
> then we're on the right path.
> Could you share details of your workload?
> In our case it was a lot of namespaces with a ton of processes
> talking to each other, forcefully killed and restarted.
> Do you see the same crash in the latest tree?
>
> PS sorry for double posts. netdev email bounced few times for me...
>

I have two machines running the experiments I noted last night. If
either blow up again I'll try this. If reverting your patch fixes it, it's
likely just a side effect of your fix (somehow...). Nothing else changed
the dst references between .15 and .25 so far as I could see.

We have a fairly bizarre/hard to reproduce workload. Full routing tables
loaded, bgp daemons running, a few hundred thousand threads, many gigabits
of direct-to-internet traffic. All on each machine.

By latest tree, you mean the very latest linux git or latest
released/stable version? Diffs are large enough that I'd likely just hit a
new crash. I might have to do that for the other panic I posted, but this
one is definitely a regression in the 3.10 stable series.
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